1. Field of the Disclosure
This disclosure relates generally to determining formation density using multiple nuclear density measurements.
2. Brief Description of the Related Art
Oil wells (wellbores) are usually drilled with a drill string that includes a tubular member having a drilling assembly (also referred to as the bottomhole assembly or “BHA”) with a drill bit attached to the bottom end thereof. The drill bit is rotated to disintegrate the earth formations to drill the wellbore. The BHA includes devices and sensors for providing information about a variety of parameters relating to the formation. Formation density is one such parameter. A conventional method of determining formation density utilizes a nuclear sensor that includes a nuclear source (such as a chemical source or a neutron generator) and a pair of spaced nuclear detectors. The accuracy of formation density measurements determined by such a conventional method is relatively high, but the spatial resolution can be low because the spatial resolution is a function of the distance between the source and the detectors and their distance from the drill bit. The spatial resolution is useful to distinguish the bed boundaries between changing formations. While spatial resolution can be improved by closely locating the source and a detector, such placement provides less accurate measurements.
The disclosure herein provides an improved apparatus and method of determining formation density utilizing at least two nuclear measurements.